swagger: advertise PathBase as OpenAPI server so Try-it-out targets the proxy prefix

Swagger UI was calling the host root (services.csbot.cz/contacts) instead of
services.csbot.cz/apps/idoklad/contacts. Emit servers=[{url: PathBase}] so the
same base that /docs runs under is prefixed to the API requests too.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Program.cs

@@ -92,6 +92,13 @@ app.UseMiddleware<ExceptionHandlingMiddleware>();
 app.UseSwagger(options =>
 {
     options.RouteTemplate = "docs/{documentName}/swagger.json";
+    // Advertise the request path base (e.g. /apps/idoklad behind the portal proxy) as the
+    // OpenAPI server so Swagger UI "Try it out" targets {pathBase}/contacts, not the host root.
+    options.PreSerializeFilters.Add((swaggerDoc, httpReq) =>
+    {
+        var basePath = httpReq.PathBase.HasValue ? httpReq.PathBase.Value : "/";
+        swaggerDoc.Servers = new List<OpenApiServer> { new() { Url = basePath } };
+    });
 });
 app.UseSwaggerUI(options =>
 {